High density magnetic recording can be attained with a perpendicular magnetic recording system, as an alternative to a conventional longitudinal magnetic recording system. In this regard, a crystalline film of a CoCr alloy system has been mainly contemplated for a magnetic recording layer of a perpendicular magnetic recording medium. In perpendicular magnetic recording, the crystal orientation of the recording layer is controlled so that the c-axis of the CoCr alloy system having a hcp structure aligns perpendicular to the film surface (i.e., the c-plane is parallel to the film surface). To obtain a higher density in the CoCr alloy system, finer grain size, reduction of dispersion of grain size distribution, and decrease in magnetic interaction between grains have been contemplated.
A method of controlling the magnetic recording layer structure to raise the recording density in a longitudinal recording medium has been proposed, for example, in U.S. Pat. No. 5,679,473. A magnetic layer in this reference, generally referred to as a granular magnetic layer, has a structure in which magnetic crystal grains are surrounded by a nonmagnetic, nonmetallic substance, such as an oxide or nitride. Because the nonmagnetic and nonmetallic grain boundary phase physically separates the magnetic grains or particles in the granular magnetic film, the magnetic interaction between the magnetic particles decreases to suppress the formation of a zigzag shaped magnetic domain wall that would be formed in a transition region of a recording bit. Thus, low noise characteristic can be achieved.
In the same vein, a granular magnetic layer is contemplated for a recording layer of a perpendicular magnetic recording medium in IEEE Trans. Mag., Vol. 36, p 2393 (2000). Specifically, this publication discloses a perpendicular magnetic recording medium comprising a ruthenium metal underlayer and a magnetic recording layer of a CoPtCrO alloy having a granular structure. A magnetic film having the granular structure is formed by reactive sputtering in an oxygen-containing atmosphere using a CoPtCr target. However, since the quantity of the generated oxide is extremely sensitive to the oxygen content of the sputtering atmosphere, it is difficult to control the quantity of the oxide formation surrounding the magnetic crystal grains. Moreover, because the magnetic crystal grain is easily oxidized, separating the material composing the magnetic crystal grains and the material composing the oxide grain boundary is extremely difficult.
Accordingly, there is a need to control the quantity of oxide contained in the granular magnetic layer to control the crystal grains and the segregation structure for ensuring a low noise characteristic. There is also a need to form a superior magnetic characteristic by removing the oxide from the magnetic crystal grain. The present invention addresses these needs.